title: Expression of merA, amoA and hao in continuously cultured Nitrosomonas europaea cells exposed to zinc chloride additions.
abstract: The effects of ZnCl2 additions on a mercuric reductase, merA, ammonia monooxygenase, amoA, and hydroxylamine (NH2OH) oxidoreductase, hao, gene expression were examined in continuously cultured Nitrosomonas europaea cells. The reactor was operated for 85 days with a 6.9 d hydraulic retention time and with four successive additions of ZnCl2 achieving maximum concentrations from 3 to 90 microM Zn2+. Continuously cultured N. europaea cells were more resistant to Zn2+ inhibition than previously examined batch cultured cells due to the presence of Mg2+ in the growth media, suggesting that Zn2+ enters the cell through Mg2+ import channels. The maximum merA up-regulation was 45-fold and expression increased with increases in Zn2+ concentration and decreased as Zn2+ concentrations decreased. Although Zn2+ irreversibly inactivated ammonia oxidation in N. europaea, the addition of either 600 microM CuSO4 or 2250 microM MgSO4 protected N. europaea from ZnCl2 inhibition, indicating a competition between Zn2+ and Cu2+/Mg2+ for uptake and/or AMO active sites. Since ZnCl2 inhibition is irreversible and amoA was up-regulated at 30 and 90 microM additions, it is hypothesized that de novo synthesis of the AMO enzyme is needed to overcome inhibition. The up-regulation of merA during exposure to non-inhibitory Zn2+ levels indicates that merA is an excellent early warning signal for Zn2+ inhibition.
authors.affiliation: School of Chemical, Biological and Environmental Engineering, 101 Gleeson Hall, Oregon State University, Corvallis, Oregon 97331-3212, USA. tyler.radniecki@oregonstate.edu
authors.forename: Tyler S
authors.initials: TS
authors.lastname: Radniecki
authors.forename: Lewis
authors.initials: L
authors.lastname: Semprini
authors.forename: Mark E
authors.initials: ME
authors.lastname: Dolan
mesh_terms: D019149:Bioreactors / Q000382:microbiology*; D018929:Cell Culture Techniques; D002712:Chlorides / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D019327:Copper Sulfate / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D008278:Magnesium Sulfate / Q000494:pharmacology; D043370:Nitrosomonas europaea / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D017967:Zinc Compounds / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D017967:Zinc Compounds; D008278:Magnesium Sulfate; C016837:zinc chloride; D010088:Oxidoreductases; C021551:mercuric reductase; C021401:hydroxylamine dehydrogenase; C045582:ammonia monooxygenase; D019327:Copper Sulfate